Gunmaking: Forging the Barrel
Let's take a look at the history and art of forging a gun barrel.
Needless to say, very early North American gun barrels were made in Europe and imported to the new world. The demand increased as did the immigrants with gunsmithing skills, allowing rifles to be made in this country. Legend holds that Lancaster, Pa., is the birthplace of the American longrifle. Back in the day, Lancaster was the westernmost frontier town in Pennsylvania. By 1759, there were four Germanic gunsmiths working in Lancaster. By virtue of it being a key trade route for western exploration, Lancaster-made rifles moved into settlements in Virginia, Tennessee and Kentucky.
In order for barrels to begin to be made in the new world, a supply of wrought (forged) iron was needed. Cast iron was too brittle. The starting stock for a gun barrel was wrought-iron skelp 40 inches long tapering from 2.25 inches to 3 inches wide and ½ inch thick. In all, the barrel skelp would weigh over 15.5 pounds.
Once the forge is prepared – using coke, not coal – the bar is heated. Although the skelp is wrought, it is fully forged along its length to help refine the metal, giving it better integrity. Throughout this process, it is important to keep the edges of the plate straight and fatten it up a bit in consideration of welding later in the process. Once the bar is fully forged, a profiled anvil is used to begin to form the bar into a round profile. To our modern-day “sensibilities,” the process of forging the barrel in this way took almost an infinite number of reheats in the forge, followed by working the shape a little followed by another reheat, etc. It took about 10 to 12 hours to forge a single rifle barrel.
When the barrel is finally formed to the proper shape, it is ready for welding. At this point, the forge needs to be cleaned to remove the impurities that might prevent a successful weld. Because of the higher heat required during this part of the process, gunsmiths must work very quickly after removing the barrel from the heat. Before removing from the heat for welding, however, the scale is removed and the edges are fluxed using anhydrous borax. When the barrel is removed from the heat, a mandrel is inserted into the hole to keep the bore from collapsing. Two different mandrel sizes are used during this process, which requires two or three people.
Welding begins in the middle of the barrel and progresses to one end. The process is then resumed in the middle toward the other end. Welding reheats are numerous because the barrel cools so quickly. Welding actually only occurs in the first few hammers after removing from the forge and inserting the tapered mandrel. Once the weld is completed, the octagonal flats are forged onto the end and worked down along the entire barrel. Forging the octagon makes the barrel stronger due to the favorable grain-flow orientation produced by the process.
The finished barrel tube weighs 6 pounds, a reduction of more than 9.5 pounds, which is due mostly to scale loss throughout the process. The barrel tube is then annealed by heating to a red-hot temperature. This is followed by putting the barrel into a soaking pit to allow it to cool more slowly. At this point, the barrel is ready for boring/reaming. Gunboring “machines” were used for this purpose. Forged boring bits and reamers were inserted into a small pulley, which was driven by a belt attached to a large wheel operated by a hand crank. The rod extends into the muzzle of the barrel, and the rapidly revolving motion of the rod enlarges the barrel, shaping it to a uniform size. As many as a dozen successively larger rods would be used before it was ready to be rifled.
The old-fashioned approach to rifling involved carving a guide pole 58 to 60 inches long and 3.5 inches in diameter. Five grooves are cut into the cylindrical pole making an entire revolution along the full distance. A rod with a cutter mounted to one end is attached to the guide pole on one end and a handle is attached to the other. The guide turns as it passes though a wooden block, and the cutter on the end of the bar cuts a small groove inside the rifle barrel. Some early rifling was land-and-groove type and some was round-bottom type. The bullet never touched the rifling.
Now you know how a rifle barrel was made from the earliest times until about the middle of the 19th century.